Re: [Patch v9 07/10] block: Add fops atomic write support

Hannes Reinecke
2024-06-21T06:13:38Z

On 6/20/24 14:53, John Garry wrote:
> Support atomic writes by submitting a single BIO with the REQ_ATOMIC set.
>
> It must be ensured that the atomic write adheres to its rules, like
> naturally aligned offset, so call blkdev_dio_invalid() ->
> blkdev_atomic_write_valid() [with renaming blkdev_dio_unaligned() to
> blkdev_dio_invalid()] for this purpose. The BIO submission path currently
> checks for atomic writes which are too large, so no need to check here.
>
> In blkdev_direct_IO(), if the nr_pages exceeds BIO_MAX_VECS, then we cannot
> produce a single BIO, so error in this case.
>
> Finally set FMODE_CAN_ATOMIC_WRITE when the bdev can support atomic writes
> and the associated file flag is for O_DIRECT.
>
> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
> Signed-off-by: John Garry <john.g.garry@oracle.com>
> ---
> block/fops.c | 20 +++++++++++++++++---
> 1 file changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/block/fops.c b/block/fops.c
> index 376265935714..be36c9fbd500 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -34,9 +34,12 @@ static blk_opf_t dio_bio_write_op(struct kiocb *iocb)
> return opf;
> }
>
> -static bool blkdev_dio_unaligned(struct block_device *bdev, loff_t pos,
> - struct iov_iter *iter)
> +static bool blkdev_dio_invalid(struct block_device *bdev, loff_t pos,
> + struct iov_iter *iter, bool is_atomic)
> {
> + if (is_atomic && !generic_atomic_write_valid(iter, pos))
> + return true;
> +
> return pos & (bdev_logical_block_size(bdev) - 1) ||
> !bdev_iter_is_aligned(bdev, iter);
> }
> @@ -72,6 +75,8 @@ static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb,
> bio.bi_iter.bi_sector = pos >> SECTOR_SHIFT;
> bio.bi_write_hint = file_inode(iocb->ki_filp)->i_write_hint;
> bio.bi_ioprio = iocb->ki_ioprio;
> + if (iocb->ki_flags & IOCB_ATOMIC)
> + bio.bi_opf |= REQ_ATOMIC;
>
> ret = bio_iov_iter_get_pages(&bio, iter);
> if (unlikely(ret))
> @@ -343,6 +348,9 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
> task_io_account_write(bio->bi_iter.bi_size);
> }
>
> + if (iocb->ki_flags & IOCB_ATOMIC)
> + bio->bi_opf |= REQ_ATOMIC;
> +
> if (iocb->ki_flags & IOCB_NOWAIT)
> bio->bi_opf |= REQ_NOWAIT;
>
> @@ -359,12 +367,13 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
> static ssize_t blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> {
> struct block_device *bdev = I_BDEV(iocb->ki_filp->f_mapping->host);
> + bool is_atomic = iocb->ki_flags & IOCB_ATOMIC;
> unsigned int nr_pages;
>
> if (!iov_iter_count(iter))
> return 0;
>
> - if (blkdev_dio_unaligned(bdev, iocb->ki_pos, iter))
> + if (blkdev_dio_invalid(bdev, iocb->ki_pos, iter, is_atomic))

Why not passing in iocb->ki_flags here?
Or, indeed, the entire iocb?

Cheers,

Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich